Na₃ScF₆: 20% Yb³⁺, 2% Er³⁺ samples were synthesized with different reaction times and reaction temperatures using the solvothermal method. We carried out a series of tests on Na3ScF6 crystals. The XRD patterns showed that the monoclinic phases of the Na₃ScF₆ samples could be synthesized under different reaction conditions, and doping with Yb³⁺ ions and Er³⁺ ions did not change the crystal structures. The SEM images showed that the sizes of the samples gradually increased with reaction time and reaction temperature. The fluorescence spectra showed that the emission peaks of the prepared samples under 980 nm near-infrared (NIR) excitation were centered at 520 nm/543 nm and 654 nm, corresponding to the ²H_11/2/⁴S_3/2→⁴I_15/2 and ⁴F_9/2→⁴I_15/2 transitions, respectively. With the increasing size of the samples, the emission intensities at 654 nm increased and the luminescence colors changed from green to red; at the same time, the red-to-green luminescence intensity ratios (IR/IG ratios) increased from 0.435 to 15.106—by as much as ~34.7 times. Therefore, this paper provides a scheme for tuning the IR/IG ratios of Na₃ScF₆: 20% Yb³⁺, 2% Er³⁺ samples by changing their sizes, making it possible to enhance the intensity of red upconversion, which has great potential for the study of color displays and lighting.

Small fluoride nanoparticles (NPs) with strong down-conversion (DC) luminescence at 1.5 μm are quite desirable for optical fiber communication systems. Nevertheless, a problem exists regarding how to synthesize small fluoride NPs with strong DC emission at 1.5 μm. Herein, we propose an approach to improve 1.5 μm emission of BaLuF₅:Yb³⁺,Er³⁺ NPs by way of combining doping Ce³⁺ ions and coating multiple BaLuF₅: Yb³⁺ active-shells. We prepared the BaLuF₅:18%Yb³⁺,2%Er³⁺,2%Ce³⁺ NPs through a high-boiling solvent method. The effect of Ce³⁺ concentration on the DC luminescence was systematically investigated in the BaLuF₅:Yb³⁺,Er³⁺ NPs. Under a 980 nm laser excitation, the intensities of 1.53 μm emission of BaLuF₅:18%Yb³⁺,2%Er³⁺,2%Ce³⁺ NPs was enhanced by 2.6 times comparing to that of BaLuF₅:18%Yb³⁺,2%Er³⁺ NPs since the energy transfer between Er³⁺ and Ce³⁺ ions: Er³⁺:⁴I_11/2 (Er³⁺) + ²F_5/2 (Ce³⁺) → ⁴I_13/2 (Er³⁺) + ²F_7/2 (Ce³⁺). Then, we synthesized BaLuF₅:18%Yb³⁺,2%Er³⁺,2%Ce³⁺@BaLuF₅:5%Yb³⁺@BaLuF₅:5%Yb³⁺ core-active-shell-active-shell NPs via a layer-by-layer strategy. After coating two BaLuF₅:Yb³⁺ active-shell around BaLuF₅:Yb³⁺,Er³⁺,Ce³⁺ NPs, the intensities of the 1.53 μm emission was enhanced by 44 times compared to that of BaLuF₅:Yb³⁺,Er³⁺ core NPs, since the active-shells could be used to not only suppress surface quenching but also to transfer the pump light to the core region efficiently through Yb³⁺ ions inside the active-shells.

A series of blue phosphorescent heteroleptic cyclometalated Ir(III) complexes with mesitylphenyl-imidazole ligands for organic light-emitting devices have been theoretically studied. We want to find their electronic structures, spectroscopic properties, and application value for organic light-emitting devices. (fppz)₂Ir(acac), (fppz)₂Ir(tpip), (dfbdp)₂Ir(fppz), (F-fppz)₂Ir(acac), (F-fppz)₂Ir(tpip), and (dfbdp)₂Ir(F-fppz) are investigated with DFT and TD-DFT approaches, where, for (fppz)₂Ir(acac), (fppz denotes 2-(5-(trifluoromethyl)-4H-pyrazol-3-yl)pyridine, and acac denotes acetylacetonate); for (fppz)₂Ir(tpip), tpip denotes tetraphenylimido-diphosphinate; and, for (F-fppz)₂Ir(acac) and (F-fppz)₂Ir(tpip), F-fppz denotes 2-(5-fluoro-4H-pyrazol-3-yl)pyridine.